Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$248.79	9.795%	$273.159	$273.16	$273.15	$273.20
Purchase #2	$140.26	7.129%	$150.2591	$150.26	$150.25	$150.30
Purchase #3	$148.79	4.549%	$155.5585	$155.56	$155.55	$155.60
Purchase #4	$182.32	7.549%	$196.0833	$196.08	$196.10	$196.10
Purchase #5	$59.39	12.150%	$66.6059	$66.61	$66.60	$66.60
Purchase #6	$239.29	9.823%	$262.7955	$262.80	$262.80	$262.80
Purchase #7	$166.81	5.275%	$175.6092	$175.61	$175.60	$175.60
7 purchase totals =	$1,185.65		$1,280.0705	$1,280.08	$1,280.05	$1,280.20